1. Field of Invention
This invention generally relates to infrared (and near-infrared) cameras and, more particularly, to enhanced dynamic-range cameras.
2. Related Art
Infrared cameras may be used to image objects and scenes by detecting radiation in the thermal infrared and/or near-infrared range. In general, the characteristics of this radiation are dependent (in part) on the temperature of the radiating object.
Infrared cameras use detectors to image objects of interest, as single images or video. One type of infrared detection system is a focal plane array (FPA). An FPA system uses an array of infrared detectors such as photodiodes or bolometers, where the output of each detector in the array is used as intensity information for an associated image pixel. Different types of detectors are sensitive to different wavelength ranges.
For some objects or scenes, there may be a wide range of in-band brightness in the field of view of interest. For example, a rocket launch scene may include both a cold rocket hardbody and an extremely hot exhaust plume. Since a typical IR camera has a brightness dynamic range of about 12-14 bits, it may be impossible to fully span such a scene with a single exposure value. The brightest or hottest parts of the image will often be saturated, while the darkest or coolest part of the scene may appear black in the image (since the signal is buried in the noise floor of the camera).
Additionally, in some circumstances the dynamic range of a scene at a particular time may not be large, but may change substantially in a short amount of time (for example, a rocket launch scene at a time just prior to launch versus a time just after launch commences). Although a single exposure value may be appropriate to image the entire scene at a particular time, if the temperature profile changes substantially, the exposure may not provide for acquisition of adequate image data at a later time.
For a particular IR camera and expected brightness range, imaging may be optimized by adjusting the camera to an optimal shutter speed or integration time. However, it may not be possible to fully encompass a scene's brightness (temperature) variations using a single integration time.